In his editorial in the March 2020 issue of Physics Today (page 8), Charles Day commented that Lord Rayleigh cited cubic millimeters for the volume of pipes but inches for their length. In the US, we measure gasoline consumption in miles per gallon, whereas in Europe, it is measured in liters per 100 kilometers, the inverse. The European metric unit has dimensions of area, but the US unit is 1/area. What is the meaning of that area? My hybrid car has a consumption of about 40 miles per gallon. The corresponding area—much easier in metric—is about 0.6 mm2. That is the cross-sectional area of a gasoline-filled pipe that, if laid along the road, will keep my car going if I scoop up the gas. It may be 2 mm2 for a gas-guzzler. I propose measuring fuel consumption in square millimeters.

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